This invention relates generally to an improvment in a liquid dispensing pump of the hand-held variety which has a plunger immobilizing means for selectively immobilizing the reciprocable pump plunger for preventing inadvertent discharge or leakage of the product during shipment and during periods of non-use of the pump.
More particularly, this invention represents an improvement over U.S. Pat. No. 3,827,606 as well as over Nos. 3,827,605 and 3,797,705.
Dispensing pumps are disclosed by these patents as having locking tongues or fingers which are deflectable by cam surfaces into the path of reciprocation of a stop shoulder provided on the plunger upon relative rotation between members containing the cams and locking fingers. The locking tongues or fingers are retracted out of such path of reciprocation when in an unstressed condition so that the plunger may be freely depressed without interference. These locking fingers or tongues are typically of a relatively stiff plastic material sufficiently flexible as to permit their deflection into the path of reciprocation of the stop shoulder to effect plunger immobilization. The tongues or fingers lie in their normal or unstressed conditions radially outwardly from such path of reciprocation; after being deflected, they return to their unstressed condition under their own elastic memory as the cam surfaces recede from the locking fingers upon such relative rotation. Sole reliance on this elastic memory of the tongues or fingers for retracting them away from the path of reciprocation of the stop shoulder to permit actuation of the pump, may render the dispensing pump inoperable if the elastic memroy is lost or diminishes during the shelf life of the product. The locking fingers cannot be expected to freely retract if, because of the cold flow of the plastic, much of the memory is lost.